Spinnable dopes for making oriented, shaped articles of lyotropic polysaccharide/thermally-consolidatable polymer blends

ABSTRACT

Spinnable dopes containing fiber-forming polymers being at least about 55% and less than about 80% lyotropic polysaccharide and at least about 20 percent and less than about 45% thermally-consolidatable polymer and a process for making oriented, shaped articles of lyotropic polysaccharide/thermally-consolidatable polymer blends by orienting the dopes and removing the solvent.

This application is a divisional of United States patent application,Ser. No. 07/337,504, filed Apr. 13, 1989 and now U.S. Pat. No.5,000,898.

BACKGROUND OF THE INVENTION

The present invention relates to composite materials and moreparticularly relates to a process for making oriented, shaped articlesincluding fibers and films of lyotropicpolysaccharide/thermally-consolidatable polymer blends having compositeutility.

High modulus fibers such as poly(p-phenylene terephthalamide) sold underthe trademark Kevlar by E. I. du Pont de Nemours and Company are usefulfor incorporation into polymeric matrix materials to produce composites.For some types of composites with thermoplastic polymer matrices, it isdesirable to coat the high modulus fiber with the matrix polymer toproduce coated fiber known as "prepreg" which can be directly moldedinto a composite by the application of heat and pressure. However, goodquality "prepregs" are difficult to produce since wetting the fiber withthe matrix polymer is often difficult. Also these prepregs are expensivedue to the separate process steps necessary to apply the matrix polymercoating.

SUMMARY OF THE INVENTION

In accordance with the invention, a process is provided for makingthermally-consolidatable shaped articles containing a substantiallycontinuous phase of lyotropic polysaccharide in the direction oforientation. The process includes forming under agitation a liquidsolution of the lyotropic polysaccharide and a thermally-consolidatablepolymer in a common solvent with the solution having a totalfiber-forming polymer concentration sufficient that the solution isbi-phasic and has an anisotropic phase and an isotropic phase. At leastabout 55% and less than about 80% by weight of the fiber-formingpolymers are lyotropic polysaccharide and at least about 20% and lessthan about 45% by weight of the fiber-forming polymers are thethermally-consolidatable polymer. The anisotropic and isotropic phasesare interdispersed with the isotropic phase being present in domainshaving a size on the average of less than about 300 microns, preferablyless than about 100 microns. The bi-phasic liquid solution is thensubjected to process steps such as extrusion in which the anisotropicphase of said solution is oriented and the solvent is removed to produceoriented, shaped articles.

In accordance with a preferred form of the process, the lyotropicpolysaccharide is cellulose triacetate having an inherent viscosity ofat least about 5.0 dl/g.

In accordance with the invention, a spinnable dope of fiber-formingpolymers in a common solvent is provided. At least about 55% of and lessthan about 80% by weight of the fiber-forming polymers are a lyotropicpolysaccharide and at least about 20% and less than about 45% by weightof the fiber-forming polymers are at least one thermally-consolidatablepolymer. The lyotropic polysaccharide and thermally-consolidatablepolymers are dissolved in the common solvent to form a bi-phasicsolution having an anisotropic phase and an isotropic phase. Theanisotropic and isotropic phases are interdispersed with the isotropicphase being present in domains having a domain size of less than about300 microns, preferably less than about 100 microns.

The spinnable dopes and process of the invention provide fibers, filmsand other shaped, oriented articles which, as spun, can be formeddirectly by the application of heat and pressure into novel consolidatedparts.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a transmission electron micrograph at 9,000× of across-section of a fiber produced in accordance with a preferred form ofthe present invention;

FIG. 2 is a transmission electron micrograph at 9,000× of a longitudinalsection of a fiber produced in accordance with a preferred form of thepresent invention;

FIG. 3 is an optical micrograph in transmission of a spin dope asemployed in Example 2; and

FIG. 4 is an optical micrograph as in FIG. 3 with crossed polarizers.

DETAILED DESCRIPTION OF THE INVENTION

The process of the invention produces oriented, shaped articles of theinvention comprised of a blend of at least one lyotropic polysaccharidepolymer and at least one thermally-consolidatable polymer. The term"lyotropic polysaccharide" is intended to refer to a class ofpolysaccharides with (1,4)-β-linkages in the backbone such as cellulose,cellulose derivatives, chitin and chitin derivatives which have a highpersistence length and function as a "rigid rod" in solution. Thus,lyotropic polysaccharides are capable with an appropriate solvent offorming an anisotropic solution, i.e., microscopic domains of thesolution are birefringent and a bulk sample of the solution depolarizesplane polarized light due to the alignment of polymer chains in thedomains which causes the light transmission properties of the domains tovary with direction.

Representative lyotropic polysaccharides for use in this invention arecellulose and cellulose derivatives and chitin and chitin derivatives.Cellulose refers to poly-1,4-β-D-glucopyranose. Cellulose derivativesare obtained by substitution of the cellulose hydroxyls throughreactions common to primary and secondary alcoholic groups such asesterification and etherification, e.g., cellulose derivatives includeethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulosetriacetate, cellulose acetate butyrate, and the like. Chitin refers topoly-N-acetyl-D-glucosamine. Though cellulose and chitin are foundnaturally with the C₅ -C₆ bond in the D-configuration, the inventiondefined herein would be just as applicable to an L-form and is notintended to be limited to the D-form. Examples of chitin derivativesinclude chitin acetate which refers topoly-N-acetyl-O-acetyl-D-glucosamine, chitin acetate/formate whichrefers to poly-N-acetyl-O-acetyl-N-formyl-O-formyl-D-glucosamine,chitosan which is obtained by de-N-acetylation of chitin and refers topoly-D-glucosamine, and chitosan acetate/formate which refers topoly-N-formyl-N-acetyl-O-acetyl-O-formyl-D-glucosamine. Preferred iscellulose triacetate which is disclosed in U.S. Pat. Nos. 4,464,323 and4,725,394, the disclosures of which are hereby incorporated byreference.

The oriented, shaped articles produced by the process of the inventioninclude at least one thermally-consolidatable polymer. The termthermally-consolidatable polymer is intended to refer to any of a widevariety of polymers which can be consolidated with application of heatand pressure by mechanisms including melting and chemical reaction.Preferred for this purpose are thermoplastic polymers, particularlythose known for use as a composite matrix. Thermoplastic polymers usefulin this invention include polyarylates such as polyetherketoneketonepolymers (PEKK), polyacrylonitrile (PAN), crystalline thermoplasticpolyamides (e.g., poly(hexamethylene adipamide) and poly(ε-caproamide)and amorphous thermoplastic polyamides. Preferred for the practice ofthe invention are thermoplastic polyamides.

The process of the invention includes forming a biphasic solution (dope)of the lyotropic polysaccharide polymer and the thermally-consolidatablepolymer in an appropriate solvent. The bi-phasic solution has ananisotropic phase containing primarily the lyotropic polysaccharidepolymer and an isotropic phase containing primarily thethermally-consolidatable polymer. For the solution to be bi-phasic, itis necessary for the concentration of the fiber-forming polymers to besufficiently high that the lyotropic polysaccharide forms an anisotropicphase which is a discrete phase separate from the isotropic phasecontaining the thermally-consolidatable polymer. However, the resultingsolids concentration should be low enough in the solvent used that thelyotropic polysaccharide polymer does not precipitate out of solution.

The solvent employed to form the biphasic solution should be selected sothat it can dissolve enough of the lyotropic polysaccharide to provide asolution of the lyotropic polysaccharide above its criticalconcentration (concentration at which the solution becomes anisotropic).It is recognized that both the molecular weight and pattern ofsubstitution of polysaccharide polymers will probably determine theirsolubility in any particular solvent and also the concentrations atwhich optical anisotropy is observed. In addition, the solvent selecteddepends on the thermally-consolidatable polymer since it must serve asbeing a common solvent for the thermally-consolidatable polymer andsingle or mixed solvents may be necessary. In a preferred form of theinvention employing cellulose triacetate and thermoplastic polyamides, amixed solvent of trifluoroacetic acid and formic acid is used. Thefiber-forming solids in the dope are made up of at least about 55percent and less than about 80 percent by weight of the lyotropicpolysaccharide and at about 20 percent and less than about 45 precent byweight of the thermally-consolidatable polymer. In general, it isnecessary for the dope to have at least 55 percent and preferablygreater than 60 percent by weight of the lyotropic polysaccharide inorder to obtain spinning continuity and good tensile strength in thearticles. Generally, less than about 20 percent of thethermally-consolidatable polymer makes it difficult to consolidate thearticles to produce a composite.

In order to obtain articles in accordance with the invention in whichthe first polymer phase containing the lyotropic polysaccharide issubstantially continuous in the direction of orientation as will bedescribed hereinafter, it is necessary for the isotropic domains in thespin dope to be finely-divided in the blend, preferably less than about300 microns, most preferably less than about 100 microns. The bi-phasicsolutions thus appear to homogeneous to the unaided eye. While this canbe achieved by adding the polymers simultaneously to the solution andmixing with strong agitation over a long period of time, it ispreferable to first add the lyotropic polymer to the solvent and thensubsequently add the thermally-consolidatable polymer. In order toprevent gross phase separation, is is usually necessary to continueagitation of the solution or to form into oriented, shaped articlesshortly after the solution is formed.

In accordance with the process of the invention, the anisotropic phaseof the biphasic solution is oriented and then the solvent is removed toproduce oriented, shaped articles. A number of techniques can be usedsuch as forming fibers by spinning or extruding the dope into films.Orientation of the anisotropic phase can be by applying shear forces toor elongational flow to the liquid solution. The techniques for solventremoval must be capable of removing the solvent from the high viscositysolutions (the solution viscosity is typically greater than 100 poise).Techniques which are suitable for this task are air-gap wet spinning andfilm extrusion processes where the solution passes through a spinneretor die into an air gap and subsequently into a coagulant bath where thesolvent is removed from the blend. In general, fiber spinning and filmextrusion processes useful for forming the lyotropic polysaccharidepolymer into high tenacity fibers and films are useful for spinning theblend fibers in accordance with the present invention. Fibers of theinvention can be produced by the method disclosed in U.S. Pat. Nos.4,464,323 and 4,725,394, the disclosures of which are herebyincorporated by reference. Liquid crystalline solutions may revert to anisotropic state when heated above a certain critical temperature andoptimum spinnability and fiber tensile properties are obtained onlybelow this temperature.

In accordance with the process described in U.S. Pat. Nos. 4,464,323 and4,725,394, for making fibers, dopes are extruded through spinnerets andthe extruded dope is conducted into a coagulation bath through anoncoagulating fluid layer. While in the noncoagulating fluid layer, theextruded dope is stretched from as little as 1 to as much as 15 timesits initial length (spin stretch factor). The fluid layer is generallyair but can be any other inert gas or even liquid which is anoncoagulant for the dope. The noncoagulating fluid layer is generallyfrom 0.1 to 10 centimeters in thickness.

The coagulation bath can be aqueous and ranges from pure water, or canbe any non-aqueous coagulating liquid. Bath temperatures can range fromfreezing to below freezing. It is preferred that the temperature of thecoagulation bath be kept below about -10° C., to obtain fibers with thehighest initial strength.

After the extruded dope has been conducted through the coagulation bath,the dope has coagulated into a fiber swollen with coagulant. The fibershould be thoroughly washed to remove salt and acid from the interior ofthe swollen fiber. Fiber-washing solutions can be pure water or they canbe slightly alkaline. Washing solutions should be such that the liquidin the interior of the swollen fiber, after washing, should beessentially neutral.

The washed yarn can be dried by air drying or heating such as in an ovenor by passing the wet yarn over multiple wraps on a pair of steam-heatedrolls.

In oriented, shaped article made by the process of the invention, thelyotropic polymer makes up a first polymer phase of the articles and thethermally-consolidatable polymer is found within a second polymer phase.Characteristic of the first polymer phase is that it is at leastsubstantially continuous in the direction of orientation of the articleswhen viewed at a magnification of 9000×. For a fiber in which thedirection of orientation is longitudinal, this structure is visible inFIG. 2 which is a transmission electron micrograph (TEM) at 9000× of alongitudinal section of the fiber made with a preferred process inaccordance with the invention. The first polymer phase appears to belighter than the darker colored second polymer phase. "Continuous in thedirection of orientation" and "longitudinally continuous" in the case offibers is intended to indicate that fibrils of the lyotropicpolysaccharide in the first polymer phase extend essentiallycontinuously in the direction of orientation or along the length of thearticle when viewed at 9000×.

Preferably, the articles are highly oriented. For fibers of theinvention, the orientation angle is preferably less than about 30°.

The second polymer phase containing the thermally-consolidatable polymerinterpenetrates the first polymer phase throughout the article as shownin FIG. 2 which is a TEM showing the structure of fiber made by apreferred process in accordance with the invention.

The oriented shaped articles of the invention are formable intoconsolidated parts by the application of heat and pressure. Knowntechniques for "prepreg" are useful for forming consolidated parts fromfibers in accordance with the invention, either by placing fibers in anappropriate mold and compressing the fibers while maintaining atemperature at or above the melting point, glass transition temperatureor reaction temperature of the thermally-consolidatable polymer to formthe consolidated parts. Unidirectional composites, composites containingfabrics woven from fibers of the invention, composites fromdiscontinuous fibers can be made by such techniques. Fibers which havebeen pulped or fibrids can be directly made into paper by a wet-layprocess. Such papers can be consolidated by heat and pressure into threedimensional composites.

In the consolidated parts, the morphology of the first polymer phase inthe oriented shaped articles used to make the composite is generallypreserved in the composite structure while the second phase isconsolidated and becomes a somewhat continuous matrix for the firstpolymer phase. In general, the mechanical properties of the elongatedshaped articles translate into the properties of the composites. Themechanical properties in the composites are equal to the propertiespredicted for short fiber reinforced composites and thus the inventionprovides the ability to make composites with excellent propertiesdirectly from as-spun fibers and films.

The examples which follow illustrate the invention employing thefollowing test methods. Parts and percentages are by weight unlessindicated otherwise.

Test Methods Transmission Electron Microscopy

Transmission electron micrographs (TEM) of the cross-section andlongitudinal section of the fiber were prepared using the followingprocedures.

Samples are prepared by first embedding a well-aligned bundle of fibers(approximately 10 filaments) in epoxy. Specimens to be cross-sectionedare most easily embedded using a BEEM size 00 capsule. A razor is usedto make both a slit across the tapered tip of the capsule along adiameter and a "V" cut in the flat top of the capsule. The fiber bundleis inserted through the two cuts so that the bundle axis coincides withthe capsule axis. The capsule is then filled with epoxy, the epoxy iscured overnight in a 70 degree C. oven, and the embedded fiber sample isremoved from the capsule. In order to prepare specimens to be sectionedlongitudinally, the two ends of a fiber bundle are taped to a TEFLONplate. A drop of epoxy is placed between the ends of the bundle andallowed to cure overnight in a 70 degree C. oven. A short segment is cutfrom the epoxied area and attached to the end of a Bakelite stub withepoxy.

Sections 2000 to 2500 Angstroms thick are cut from the embedded fiberspecimens using a Du pont MT6000 Ultramicrotome and a diamond knife at acutting speed of 0.7 mm/sec. In the case of cross-sections, the cuttingdirection is essentially perpendicular to the long axis of the fiber,and in the case of longitudinal-sections, the cutting direction isessentially parallel to the long axis of the fiber. The fiber sectionsare then transferred to 3 mm diameter, 200 mesh electron microscopegrids.

JEOL 200CX TEM/STEM equipped with a goniometer specimen stage andoperated at an accelerating potential of 200 keV is used to examine thefiber sections at the desired magnification (an objective aperature maybe used to improve contrast) and the image is recorded on electron imagefilm. The film is placed in a photographic enlarger where the recordedimage is enlarged 3× and projected onto photographic film from which apositive print is made.

Tensile Properties

Yarn properties are measured at 21.1° C. and 65% relative humidity whichhave been conditioned under the test conditions for a minimum of 16hours. Yarn denier is calculated by weighing a known length of yarn. Thetenacity (grams/denier, gpd), elongation(%), initial modulus (gpd) asdefined in ASTM D2101 are calculated from the load-elongation curves at10% strain per minute on sample lengths of 25.4 cm and the measured yarndenier. Before each test, the yarns were twisted.

Where single filament properties are reported, tensile properties aredetermined similarly with a guage length of 2.54 cm for tenacity andelongation and 25.4 cm for modulus. The denier of a single filament wascalculated from its fundamental resonant frequency, determined byvibrating a 4.1 cm length of fiber under tension with changing frequency(ASTM D2577 Method B).

Fiber X-ray Orientation Angle

A bundle of filaments about 0.5 mm in diameter is wrapped on a sampleholder with care to keep the filaments essentially parallel. Thefilaments in the filled sample holder are exposed to an X-ray beamproduced by a Philips X-ray generator (Model 12045B) operated at 40 kvand 40 ma using a copper long fine-focus diffraction tube (Model PW2273/20) and a nickel beta-filter.

The diffraction pattern from the sample filaments is recorded on KodakDEF Diagnostic Direct Exposure X-ray film (Catalogue Number 154-2463),in a Warhus pinhole camera. Collimators in the camera are 0.64 mm indiameter. The exposure is continued for about fifteen to thirty minutes(or generally long enough so that the diffraction feature to be measuredis recorded at an Optical Density of ˜1.0).

A digitized image of the diffraction pattern is recorded with a videocamera. Transmitted intensities are calibrated using black and whitereferences, and gray level is converted into optical density. A dataarray equivalent to an azimuthal trace through the two selectedequatorial peaks is created by interpolation from the digital image datafile; the array is constructed so that one data point equals one-thirdof one degree in arc.

The Orientation Angle is taken to be the arc length in degrees at thehalf-maximum optical density (angle subtending points of 50 percent ofmaximum density) of the equatorial peaks, corrected for background. Thisis computed from the number of data points between the half-heightpoints on each side of the peak. Both peaks are measured and theOrientation Angle is taken as the average of the two measurements.

Inherent Viscosity

Inherent Viscosity (IV) is defined by the equation:

    IV=ln(ηrel)/c

where c is the concentration (0.5 gram of polymer in 100 ml of solvent)of the polymer solution and ηrel (relative viscosity) is the ratiobetween the flow times of the polymer solution and the solvent asmeasured at 30° C. in a capillary viscometer. The inherent viscosityvalues reported for CTA are determined using hexafluoroisopropanol.

Domain Size in Spin Dopes

Spin dopes were examined with optical microscopy to determine thebiphasic nature of these solutions. For the CTA, PAN, nitric acidsolution, the dope was placed between two glass slides. The sample waspressed, using hand pressure, to facilitate a thin sample. The edges ofthe slides were sealed with Parafilm (TM), to prevent loss of solvent.The sample was allowed to relax overnight at room temperature.

The samples were observed with polarized and cross polarized light usinga Nikon polarizing optical microscope equipped with a camera. It hasbeen shown that static (relaxed) isotropic solutions when placed betweencrossed polarizing elements will transmit essentially no light. However,anisotropic dopes will transmit light and a relatively bright field isobserved. Since these solutions are composed of two phases, one beingistotropic and one being anisotropic, the two phases can bedistinguished by comparison of observation between polarized and crosspolarized light. The samples were viewed and photographed at 100x.Polariod type 57 3000 ASA film was used. Size of the isotropic domainswas determined by measurement of isotropic domains on the photographs.

EXAMPLE 1

Cellulose triacetate (CTA, having an acetyl content of 43.7% and aninherent viscosity of 6.0 dl/g in hexafluoroisopropanol at 30 degreesC.) and the polyamide (a copolymer of hexamethylene diamine,bis(p-aminocyclohexyl)methane, isophthalic acid, and terephthalic acidin a 96/4/70/30 mole ratio) were dried overnight in a vacuum oven at 80degrees C. under a nitrogen purge. An organic solvent composed oftrifluoroacetic acid (TFAA) and formic acid (FA) in a 79/21 weight ratiowere mixed together in a glass beaker. 65 parts by weight of the TFAA/FAsolvent mixture was then added to 24.5 parts by weight of CTA in a 500cc twin blade shear mixer. The mixer was pre-cooled to -5 degrees C. byan external refrigeration unit in order to minimize degradation of theCTA by the acid. Mixing was begun and typically continued for 2 hours inorder to thoroughly wet the CTA. 10.5 parts by weight of the polyamidewas then added to the mixer and mixing was continued until the next day.Occasionally the mixer was opened and a spatula was used to scrape anyundissolved polymer that was stuck to the mixer walls and blades backinto the rest of the spin dope. The resulting spin dope consisted of 35weight percent polymer (70 weight percent CTA/30 weight percentpolyamide) in 65 weight percent solvent (79 weight percent TFAA/2lweight percent FA). The spin dope appeared homogeneous and exhibitedshear opalescence. In addition, long fibers could be pulled from thespin dope with a spatula.

The spin dope was then transferred to the spin cell and spun at roomtemperature and at a constant throughput rate of 0.2 ml/min through aspinneret with ten 0.005 inch diameter holes, across a 0.75 cm air-gap,and into a coagulating bath of methanol chilled to -10 degrees C. Thefiber was wound up on a bobbin at a speed of 6.3 m/min resulting in aspin-stretch factor of 4. The fiber was washed continuously on thewindup bobbin with water, soaked in water overnight to extract residualsolvent, and subsequently air dried.

The yarn tensile strength/elongation/modulus of the as-spun compositefiber (having three twists/inch) was 4.1 gpd/5%/100 gpd. The orientationangle was 18 degrees. Examination of the cross-section of the fiber at9000× by transmission electron microscopy (TEM) revealedinterpenetrating phases of CTA and polyamide. TEM examination of alongitudinal-section of the fiber at 9000× revealed that the CTA and thepolyamide were continuous along the length of the fiber.

EXAMPLE 2

Cellulose triacetate (CTA, having an acetyl content of 43.7% and aninherent viscosity of 6.0 dl/g in hexafluoroisopropanol at 30 degreesC.) and polyacrylonitrile (PAN) were dried overnight in a vacuum oven at80 degrees C. under a nitrogen purge. An inorganic solvent composed ofnitric acid and water in a 87.5/12/5 weight ratio were mixed together ina glass beaker. 70 parts by weight of the aqueous nitric acid mixturewas then added to 21 parts by weight of CTA and 9 parts by weight of PANin a 500 cc twin blade shear mixer. The mixer was pre-cooled to 5degrees C. by external refrigeration unit in order to minimizedegradation of the CTA by the acid. Mixing was begun in the morning andcontinued until the next day. Occasionally the mixer was opened and aspatula was used to scrape any undissolved polymer that was stuck to themixer walls and blades back into the rest of the spin dope. Theresulting spin dope consisted of 30 weight percent polymer (70 weightpercent CTA/30 weight percent polyacrylonitrile) in 70 weight percentsolvent (87.5 weight percent nitric acid/l2.5 weight percent water). Thespin dope appeared homogeneous and exhibited shear opalescence. FIGS. 3and 4 are optical micrographs of the spin dope showing that the twophases are interdispersed. The width of domains of the isotropic phaseis on the order of 100-300 microns. In addition, long fibers could bepulled from the spin dope with a spatula.

The spin dope was then transferred to the spin cell while pulling vacuumto deaerate and spun at room temperature and at a constant throughputrate of 0.4 ml/min through a spinneret with ten 0.005 inch holes, acrossa 1 cm air-gap, and into a coagulating bath of 75/25 volume ratiomethanol/water chilled to 0 degrees C. The fiber was wound up on abobbin at a speed of 12.8 m/min resulting in a spin-stretch factor of 4.The fiber was washed continuously on the windup bobbin with water,soaked in water overnight to extract residual solvent, and subsequentlyair dried.

The filament tensile strength/elongation/modulus of the as-spuncomposite fiber was 6.1 gpd/6%/l29 gpd. The orientation angle was 27degrees. Referring to FIG. 1, examination of the cross-section of thefiber at 9000× by transmission electron microscopy (TEM) revealedisolated domains of CTA. TEM examination of a longitudinal-section ofthe fiber at 9000× as shown in FIG. 2 revealed that the CTA and thepolyacrylonitrile were continuous along the length of the fiber.

We claim:
 1. A spinnable dope consisting essentially of fiber-forming polymers in a common solvent, at least about 55% of and less than about 80% by weight of said fiber forming polymers comprising a lyotropic polysaccharide and at least about 20% and less than about 45% by weight of said fiber-forming polymers being at least one thermally-consolidatable polymer, said lyotropic polysaccharide and said thermally-consolidatable polymers being dissolved in said common solvent to form a bi-phasic solution having an anisotropic phase and an isotropic phase, said anisotropic and isotropic phases being interdispersed to form domains with said isotropic phase having a domain size of less than about 300 microns.
 2. The spinnable dope of claim 1 wherein at least about 60% of said fiber-forming polymers is said lyotropic polysaccharide.
 3. The spinnable dope of claim 1 wherein said lyotropic polymer is cellulose triacetate having an inherent viscosity of at least about 5 dl/g.
 4. The spinnable dope of claim 1 wherein said thermally-consolidatable polymer is selected from the class consisting of thermoplastic polymers.
 5. The spinnable dope of claim 1 wherein said thermally-consolidatable polymer is selected from the class consisting of thermoplastic polyamides.
 6. The spinnable dope of claim 1 wherein said common solvent comprises a single solvent.
 7. The spinnable dope of claim 1 wherein said common solvent comprises a mixed solvent.
 8. The spinnable dope of claim 3 wherein said thermally-consolidated polymer is selected from the class consisting of polyarylates and said common solvent is aqueous nitric acid.
 9. The spinnable dope of claim 3 wherein said thermally-consolidated polymer is selected from the class consisting of thermoplastic polyamides and said common solvent is a mixed solvent of trifluoracetic acid and formic acid.
 10. The spinnable dope of claim 1 wherein said domain size of said isotropic phase is less than about 100 microns. 